1. Field of the Invention
This invention relates to new, dual promoted, high surface area, iron/manganese spinel compositions promoted with copper and with a Group IA or Group IIA metal, their preparation and use. More particularly, this invention relates to new, unsupported, single phase Fe-Mn spinel compositions, dual promoted with copper and a Group IA or Group IIA metal, their preparation and use as pelletized catalysts in fixed-bed Fischer-Tropsch process for producing C.sub.5 + hydrocarbons from mixtures of CO and H.sub.2. These catalysts have a surface area greater than about 30 M.sup.2 /g in which the atomic ratio of Fe to Mn is greater than 2:1.
2. Background of the Disclosure
Fischer-Tropsch processes have long been known to produce gaseous and liquid hydrocarbons containing C.sub.2 -C.sub.4 olefins. Because of the importance of C.sub.2 -C.sub.4 olefins, particularly as feedstocks for the chemical industry, modifications of the Fischer-Tropsch process are constantly being pursued toward the goals of maximizing C.sub.2 -C.sub.4 olefin selectivity with the particular objective of maintaining high catalyst activity and stability under the reaction conditions and with iron based catalysts, in minimizing selectivity to CO.sub.2. The main thrust of the efforts in this area has been in the area of catalyst formulation.
Coprecipitated and/or supported iron-based catalysts, including those containing manganese, are known for producing C.sub.2 -C.sub.4 olefins. Examples of disclosures in the art directed to such iron-manganese catalysts and/or alloys include: W. L. vanDijk, et al., Appl. Catal., 2, 273 (1982); Eur. Pat. Appl. 49888 to Ruhrchemie (1981); H. J. Lehman, 73rd AIChE Meeting Paper #103D; W. D. Deckwer, et al., Chem. Ing. Tech., 53 (10), 818 (1981); V. Rao and R. Gormley, Hydrocarbon Processing, November (1981); H. Kolbel and K. Tillmetz, U.S. Pat. No. 4,177,203 (1970); EPO Patent Publication 0,071,770; U.S. Pat. No. 2,605,275; U.S. Pat. No. 2,850,515; Prepr. Div. Pet. Chem. Am. Chem. Soc. (1978) 23(2) pp 513-20; Intersoc. Energy Convers. Eng. Conf. 1978, 13(1) pp 482-6; U.S. Pat. No. 4,186,112; Ep 49,888; React. Kinet. Catal. Lett. 1982, 20(1-2) pp 175-80; U.S. Pat. No. 2,778,845; Khim. (1) Tekhnol. Tooliv i Masel (Russ.) 10(6) 5-10 (1965); UK Patent Appln. 2,050,859 A; German Patent Appln. DT 2919-921; Prace Ustavu Vyzkum Paliv 8, p. 39-81 (1964) (Czech).
An iron-manganese spinel of the formula, Fe.sub.2 MnO.sub.4, is reported as a catalyst component formed during Fischer-Tropsch synthesis in which a coprecipitated Fe/Mn oxide catalyst is initially employed in Applied Catalysis 5 (1983) pp. 151-170.
U.S. Pat. No. 2,778,845 to McGrath, et al. discloses a non-spinel type, low surface area, sintered catalyst composition containing reduced or metallic iron as a major component. These compositions are used to synthesize hydrocarbons from mixtures of hydrogen and carbon monoxide and are formed via a high temperature fusion in an electric arc furnace. The sintered or fused composition must then be reduced, preferably in hydrogen, to form the metallic iron-containing catalyst. U.S. Pat. No. 2,605,275 to Kearby, et al. discloses forming hydrocarbons from mixtures of CO and H.sub.2 employing low surface area, sintered, spinel type catalysts containing iron and a divalent metal of the general formula Fe.sub.2 MeO.sub.4 wherein Me is the divalent metal. The molar ratio of Me to Fe.sub.2 O.sub.3 is preferably greater than 1:1. Thus, the ratio of Fe/Me is no greater than 2/1 and preferably less than 2/1.
U.S. Pat. No. 3,970,738 to Matsui, et al. discloses an iron oxide composition containing a minor amount of manganese oxide and a process for making same. The object of the invention in this disclosure is stated as being able to provide iron oxide products substantially free from manganese compounds as impurities. The upper limit on the manganese component of these iron oxide products is taught and claimed as being less than 0.2 weight percent calculated as MnO. Maiti, et al. in "Iron/Manganese Oxide Catalysts for Fischer-Tropsch Synthesis. Part I: Structural and Textural Changes By Calcination, Reduction and Synthesis", J. Applied Catalysis, v5, p. 151-170 (1983) discloses the use of iron-manganese containing catalysts in a Fischer-Tropsch process to produce olefins. Spinel compositions are suggested as being present in the catalysts used in this reference. This reference does not disclose the use of copper and potassium promoted spinels, or synthesis of higher hydrocarbons.
Van Dijk, et al. in "Effects of Manganese Oxide and Sulfate on the Olefin Selectivity of Iron Catalysts in the Fischer-Tropsch Reaction", J. Applied Catalysis, v2, p. 273-288 (1982) disclose a Fischer-Tropsch catalyst which, on page 277, is set forth as a mixture of alpha iron oxide, alpha iron hydroxide and Mn.sub.2 O.sub.3. This reference discloses that these catalysts produce substantially more than about 20% methane make and an equilibrium methane selectivity (on page 283) of over 30%. U.S. Pat. No. 4,177,203 to Kolbel, et al. discloses, in line 6-9 of column 3, a Fischer-Tropsch process using a catalyst which contains more than 50% manganese and less than 50% iron. This process produces low molecular weight olefins. Kolbel, et al. in "Feedstock For Chemical Industry By Selective Fischer-Tropsch-Synthese", 1978 Society of Automotive Engineers, p. 482-486, disclose a Fischer-Tropsch catalyst consisting of a precipitated mixture of gamma Mn.sub.2 O.sub.3 and alpha Fe.sub.2 O.sub.3 inserted in the manganese oxide lattice. Thus, the catalyst composition of this reference consists of mixed oxide phases. Further, the ratio of manganese to iron oxide of the catalyst disclosed therein is set forth as being between 8 and 10.
European Patent 71,770 discloses iron-manganese catalysts promoted with potassium, wherein the maximum ratio of iron to manganese is 1:2. Compositions set forth in the Tables on pages 11 and 13 of this reference disclose iron/manganese ratios of 1:3.
Bruce, et al. in "Light Olefin Production From CO/H.sub.2 Over Silica Supported Fe/Mn/K Catalysts Derived From a Bimetallic Carbonyl Anion, [Fe.sub.2 Mn(CO).sub.12 ]", React. Kinet. Catal. Lett., v. 20, Nos. 1-2, p. 175-180 (1982) disclose olefin production using supported catalysts prepared from carbonyl precursors, with silica being the support. Methane selectivity incurred with the use of this catalyst in Fischer-Tropsch hydrocarbon synthesis reactions is disclosed as about 31% (unpromoted) and 18% (potassium promoted).
Jenson, et al. in "Studies on Iron-Manganese Oxide Carbon Monoxide Catalysts; I. Structure of Reduced Catalyst", J. of Catalysts, v. 92, p. 98-108 (1985) disclose iron-manganese catalysts showing enhanced selectivity for low molecular weight olefins from synthesis gas. The reduced catalyst composition is disclosed as having been found to be an alpha iron oxide and a manganese (II oxide) as separate phases, with the manganese oxide phase containing some divalent iron oxide in solid solution. Maiti, et al. in "Iron/Manganese Oxide Catalysts For Fischer-Tropsch Synthesis. Part II, Crystal Phase Composition, Activity and Selectivity" J. Appl. Catal. 16 (2) 215-25 (1985) disclose structural changes in the Fe-Mn oxide system under synthesis gases as a function of various pretreatments.
French Patent 2,554,433 discloses passing a mixture of H.sub.2 and CO over a spinel catalyst having the general formula of Li.sub.x Cu.sub.1-x Fe.sub.5 O.sub.8 and French Patent 2,553,399 discloses a similar process employing a catalyst having the general formula of Cu.sub.x Mn.sub.1-x Fe.sub.y Cr.sub.1-y O.sub.4.
U.S. Pat. No. 4,621,102 discloses the catalyst used in this process. However, the process disclosed in that patent is a slurry process wherein the catalyst particle size is indicative of slurried iron catalyst particles, that is, less than about 50 .mu.m.
Finally, Pennline, et al. in "The Effect of Activation and Promotion on a Fischer-Tropsch Catalyst" 189th ACS National Meeting (Miami Beach 4-28-5/3/85) ACS Div. Fuel Chem. Prep. 30# 2:310-17 (1985) disclose a Fischer-Tropsch catalyst employed in a slurry reactor employing catalysts containing 21% iron 79% manganese oxide activated in-situ, under various conditions.
However, none of the references cited above describe a Fischer-Tropsch hydrocarbon process employing an unsupported single phase Fe/Mn spinel catalyst having an Fe:Mn atomic ratio above 2:1 and a surface area greater than about 30 M.sub.2 /g and being dual promoted with both copper and a Group IA or IIA metal promoter agent.
Co, Ru and Fe catalysts are used to produce high molecular weight hydrocarbons from CO and H.sub.2 in fixed bed reactors. Co and Ru do not catalyze the water-gas shift reaction (CO+H.sub.2 O .fwdarw.CO.sub.2 +H.sub.2) at synthesis temperatures, while Fe catalysts do (CO.sub.2 selectivity &gt;30%). Fe catalysts produce a more olefinic product, but high recycle ratios are required to decrease the CO.sub.2 production rate. It is very desirable to develop Fe-based catalysts that can produce high C.sub.5 + yields with low shift selectivity.
Iron catalysts coming close to fulfilling these requirements are used commercially at SASOL. These are Fe-based catalysts promoted with Si, K, and Cu; they are reported to produce .about.20% CO.sub.2 and high molecular weight products. Mn is apparently not a crucial component in such catalysts. Our uniquely prepared, high surface area Fe-Mn spinels, show unexpected and desirable behavior. They are the subject of a recently filed patent application (U.S. Ser. No. 814,040, filed Dec. 27, 1985) that describes their use as fine powders in a slurry reactor to produce C.sub.5 -C.sub.15 .alpha.-olefins from CO and H.sub.2. In slurry reactors, these catalysts convert 40% of the feed CO to CO.sub.2 at 270.degree. C., 75 psi, and 2/1 H.sub.2 /CO. Other researchers have reported that Fe-Mn catalysts prepared differently from these can be useful to produce C.sub.2 -C.sub.4 olefins from CO and H.sub.2 ; they do not report low shift activity or high C.sub.5 + selectivities. The instant invention teaches the unusual combination of low shift activity, low CH.sub.4 selectivity and high C.sub.5 + yields using pelletized high-surface area Fe/Mn spinels, promoted with K and Cu, and run in fixed bed reactors at low temperature (200.degree.-240.degree. C.), and high pressure (150-450 psi).